(a) Field of the Invention
The present invention relates to the vibration system of a pickup cartridge of a record player, and more particularly it pertains to a vibration system of a pickup cartridge having a damper which is deformed with the application of a vertical tracking force.
(b) Description of the Prior Art
In a pickup cartridge having a damper in the vibration system, in general, a required amount of vertical tracking force is applied to the stylus as the stylus tip is brought into contact with the record groove on a record disc surface, whereby the damper is caused to be deformed for an amount corresponding to the vertical tracking force applied actually during the play of the record disc. As a result, the stylus tip and the cantilever having this stylus at its forward end portion will be rendered to the state of being moved upwardly about the fulcrum of the vibrating system.
Therefore, an arrangement has been considered so that in the non-tracing state, wherein the stylus tip is free of any vertical tracking force (which will hereinafter be referred to as VTF), both the stylus tip and the cantilever are held in the state of having been displaced or moved downwardly for a required amount by taking the VTF into account, and that, in the state wherein the stylus tip is applied with a VTF as it is brought into contact with the record groove on a record disc surface, a preliminarily intended vertical tracking angle can be obtained.
As the means of imparting such displacement to the vibration system of a pickup cartridge, there has been known the arrangements as shown in, for example, FIGS. 1 and 2.
The examples of vibration systems of pickup arm cartridges shown in FIGS. 1 and 2, are simply arranged as follows: a plate-like armature 3 is fixed to the rear end portion of a cantilever 2 having a stylus tip 1 at its forward end portion; a damper 4 is disposed rearwardly of both the rear end portion of the cantilever 2 and the armature 3; a holder 5 is disposed rearwardly of the damper 4; an end of a tension wire 6 is fixed to the rear end portion of the cantilever 2; the other end portion of the tension wire 6 is passed through the damper 4 to extend through the holder 5; and this other end of the tension wire 6 is fixed in a tensioned state within the holder 5. In this arrangement, the vibration system shown in FIG. 1 is arranged so that the front surface 4a of the damper 4 is formed to provide a slanted surface, by decreasing the thickness of the damper 4 as it goes from the upper edge to the lower edge, so as to impart a displacement to both the stylus tip 1 and the cantilever 2. Also, the vibration system shown in FIG. 2 is arranged so that by slanting the front surface 5a of the holder 5 a similar displacement is imparted.
Now, in the above-mentioned means of imparting a displacement, the damper 4, which, ordinarily, is made of an elastic member such as rubber or synthetic rubber, is brought to a state in which a required pressure bias is applied at the time of tracing the record groove of a record disc. Such an elastic member, i.e., the damper mentioned above, has a non-linear stress-strain characteristic as shown in FIG. 3. If it is assumed here that the pressure in the direction of VTF and also the displacement caused by this pressure take place in the positive direction, it will be noted that, in the instance of FIG. 1, the displacement caused by the pressure applied in the negative direction becomes greater than the displacement caused by the pressure in the positive direction. In contrast thereto, in the instance of FIG. 2, the displacements related to both the positive and negative pressures are of such characteristic that they are equal to each other, as shown by the dotted line in FIG. 3.
In each case, it will be noted that, at the time of tracing a record groove, the damper 4 is rendered to the state in which a predetermined pressure bias has been applied, as shown by point C of FIG. 3, and that, accordingly, the stress-strain characteristic of the elastic member is no longer centered around zero. Accordingly, such non-linear strain as indicated by .DELTA.D and .DELTA.D' relative to the upward and downward movements of the stylus, respectively, are exhibited, adversely affecting the movement of the armature, and accordingly degrading the quality of the sounds reproduced.
Furthermore, in the prior art, there are the drawbacks that, in the arrangement of FIG. 1, the damper 4 is difficult to mold, whereas in the arrangement of FIG. 2, the machining of the holder 5 is troublesome.